The present invention relates generally to digital information systems. More particularly, the present invention relates to code division multiple access (CDMA) based transmission and reception systems for low latency, high-quality, voice applications.
The transmission of digital information and data between systems has become an essential part of commonly used systems. With such systems, information content is transmitted and received in digital form as opposed to analog form. The transmission of voice information across long distances has long been associated with well known analog transmission techniques. These techniques include, for example, the traditional plain old telephone system (POTS) network, conventional wireless VHF/UHF two-way communications systems, and the like. The modern digital form of communication and signal processing techniques offer numerous advantages and are rapidly replacing the traditional means. In most applications, the user has no perception of the digital nature of the information being received. CDMA based digital cellular systems are among the most rapidly growing of the modern forms of digital communications.
Prior art FIG. 1 shows a CDMA digital cellular system 100. System 100 typically includes many hundreds of mobile cellular telephones (e.g., xe2x80x9ccell phonesxe2x80x9d) communicatively coupled to a base station in a geographic area. FIG. 1 depicts a single such base station 104 and a single cell phone 102. The transmission system uses an RF communications channel 106 to link the base station 104 with the cell phone 102.
In typical applications, many hundreds of cell phones share the communications link 106 to the geographical area""s base station 104. Digital signal processing techniques allow the efficient use of the limited communications channel bandwidth by the multiple cell phones. CDMA is, in part, a signal processing technique which provides for the efficient multiplexing of voice and other data into discrete time and frequency based packets of information for transmission between each of a plurality of cell phones (e.g., cell phone 102) and the shared base station 104.
Although the CDMA algorithms are very efficient, the bandwidth of the communications channel 106 is finite. As with other digital communications systems, there are times when two-way communications using system 100 will suffer some amount of signal degradation during the transmission from the originating device to the receiving device.
This degradation can have many causes. For example, bad weather conditions may reduce the effective bandwidth available for communications channel 106. As another example, system 100 may at times require the transmission of large amounts of signaling and call maintenance data in addition to the voice traffic. In both these cases, the available bandwidth for transmitting voice information may at times fall below some optimal level. This degradation often results in the loss of some voice information, some distortion in the voice signal, or some noticeable noise in the received signal (e.g., as in the case of a wireless telephone). Generally, the more significant the loss of information at the receiving device, the more objectionable performance of the communications system.
Hence, the basic cause of the degradation is the fact that, at certain times, there exists more voice information than available bandwidth for transmission of the voice information, causing system 100 to reduce (e.g., throw away) some amount of voice information to fit within the available bandwidth, and the fact that at certain times, the time required to implement the various signal processing algorithms induce an objectionable degree of latency into the bi-directional communication (e.g., conversation).
In an effort to help correct this problem, the CDMA communications industry has adopted various signal encoding/decoding techniques which counteract the effects of signal degradation and improve or ensure the integrity of the information at the receiving device, and signal processing techniques which are fast executing to reduce latency. Hence, many digital communications systems available on the market use encoding/decoding methods that are each able to accomplish reasonable communication quality under normal operating conditions. However, while these encoding/decoding methods help ensure the integrity of the received information, they also tend to add a larger than desired amount of latency to communications system as the encoding/decoding algorithms are processed. Examples include standards such as IS-95A, J-STD-008, TIA/FIA-95-B, etc., which describe the multiplexing an demultiplexing primary, secondary and signaling traffic to and from an underlying physical layer traffic channel in a CDMA system.
Thus, what is needed is a solution which tailors the encoding/decoding techniques to maximize voice quality of the CDMA communications system. What is required is a method which seamlessly functions with the dynamically adjusting parameters of the encoding/decoding algorithms utilized in CDMA communications systems. What is required is a solution capable of transmitting the required side band data without adding significant latency to the voice communications data. In addition, the required solution should not overly reduce the observed voice signal quality. The present invention provides a novel solution to the above requirements.
The present invention provides a solution which tailors the encoding/decoding techniques to maximize voice quality of the CDMA communications system. The present invention provides a method and system which seamlessly functions with the dynamically adjusting parameters of the encoding/decoding algorithms utilized in CDMA communications systems. The present invention provides a solution capable of transmitting the required signaling data without adding significant latency to the voice communications data and without overly reducing the observed voice signal quality.
In one embodiment, the present invention is implemented as a CDMA communications station in a bidirectional CDMA based wireless digital communications system. The CDMA communications station includes a signal encoder adapted to encode signaling information into a signaling packet. A vocoder (voice encoder) is also included to encode voice information at a variable data rate and process the voice information into a voice packet. A multiplexer is coupled to receive the voice packet from the voice encoder and coupled to receive the signaling packet from the signal encoder. The multiplexer combines the voice packet and the signaling packet into a traffic frame. A transmitter is coupled to the multiplexer for transmitting the traffic frame as received from the multiplexer.
An early indication describing the data rate and the size of the voice packet produced by the voice encoder is generated and provided to the multiplexer. The multiplexer subsequently uses the early data rate indication from the voice encoder to preconfigure the traffic frame for the variable data rate voice packet. The preconfigured traffic frame is built to readily accept the voice packet once the processing of the voice packet by the voice encoder is complete. This allows the traffic frame to be sent to the transmitter for transmission immediately upon reception of the voice packet from the voice encoder, thereby reducing the latency of the digital communications system.